This invention relates to a cue signal generating circuit for a recording apparatus such as a tape recorder.
In recording an audio signal, a tape recorder generally records a cue signal together with a desired audio signal for a prescribed period of time in order to rapidly detect a recorded portion of a desired audio signal. The cue signal has a very low frequency of about several tens of Hz, compared to the audio signal. Accordingly, it is not reproduced when the audio signal is reproduced. In order to detect the desired recorded portion, a playback head is in contact with a tape when the tape is caused to travel at a high speed. A tape travelling speed in a fast forward mode or a rewind mode is faster than that in the record mode by approximately several tens times. Accordingly, in the playback mode, the frequency band of the cue signal, which is much lower than the playback frequency band of the tape recorder, is increased to reproduce the cue signal. Assume now that a cue signal of 30 MHz is recorded for 10 seconds and the tape speed in the fast forward and rewind modes is 20 times that in the record mode. In this case, the cue signal is reproduced as a signal of 600 Hz for 0.5 second when the tape is caused to travel at a high speed. At the time of high speed tape travel, the frequency of the audio signal becomes excessively high and is not reproduced. By counting the number of the detections of the cue signal, a desired recorded portion is detected. A conventional cue signal generating circuit uses a one-shot multivibrator and a low frequency signal oscillator. The low frequency oscillator, which produces a sinusoidal wave signal of several Hz to several tens of Hz, is energized by a signal with a prescribed time duration produced from the multivibrator. The low frequency signal is applied as a cue signal to a recording head for a prescribed period of time. When the time constant of a multivibrator is fixed to a relatively long period of time (several seconds), it is difficult to keep and consistent the recording time of the cue signal. To provide a low frequency oscillator with stable frequency and amplitude, a number of components are required. Thus the chip size becomes large in fabricating the integrated oscillator. When the frequency of the sinusoidal wave signal is too low, the waveform of the signal is easily distorted when it is recorded, so that the merit of using the sinusoidal waveform is decreased.